1. Field of the Invention
The present invention relates to an evaluation pattern and method for evaluation of lateral hillocks formed on metal interconnections.
2. Description of the Related Art
As known in the art, metal interconnections, typically formed of aluminum or aluminum alloy, often suffer from unintended formation of protrusions called “hillocks” which is caused by abnormal metal crystal growth due to the thermally-induced stress resulting from annealing processes performed after the deposition and patterning of the metal interconnections in the manufacture. Especially, lateral hillocks growing in the direction along the substrate surface, which are likely to formed on the sides of wide metal interconnections, may cause short-circuiting between adjacent interconnections; the size of a large lateral hillock may reach 1 μm or more, which is significant in view of the interconnection spacing of recent integration circuits.
Japanese Laid Open Patent Application No. JP-A-Heisei, 1-234567 discloses an interconnection pattern for addressing the short-circuiting caused by lateral hillock formation. FIG. 5 shows the disclosed interconnection pattern. It should be noted that FIG. 5 is a plan view of the disclosed interconnection pattern.
As shown in FIG. 5, the conventional interconnection pattern 1 includes a wide interconnection 2 (with a width of 10 μm or more, for example), and narrow interconnections 3 (with a width less than 10 μm, for example) separately provided along the sides of the wide interconnections 2. The narrow interconnections 3 are almost free from the lateral hillock due to the narrow width thereof.
The interconnection pattern 1 effectively resolves the short-circuiting potentially caused by the lateral hillocks; there is no problem even if a hillock 4 grows from the side of the wide interconnection 2 to be in contact with the narrow interconnections 3, since the voltage levels of the narrow interconnections 3 are identical to that of the wide interconnection 2. It should be noted that neighboring interconnections 5 are also free from lateral hillocks, since the neighboring interconnections 5 are opposed to the narrow interconnections 3 instead of the wide interconnection 2; the narrow width of the narrow interconnections 3 effectively suppresses the lateral hillock formation on the neighboring interconnections 5.
Although the conventional interconnection pattern 1 effectively addresses the problem of short-circuiting between adjacent interconnections caused by the lateral hillocks, the interconnection pattern 1 is not suitable of manufacturing process evaluation from the viewpoint of lateral hillock formation. The above-mentioned interconnection pattern 1, which is not structured to promote the formation of lateral hillocks, does not provide a sufficient number of lateral hillocks for manufacturing process evaluation in light of the usual lateral hillock formation frequency.
The conventional process evaluation in connection with the lateral hillock formation, which involves manually observing a small number of lateral hillocks with an optical microscope and so on, also suffers from poor efficiency, taking a long time for hillock formation evaluation.